Fluorinated greenhouse gases, carbon dioxide, methane, and nitrous oxide are collectively known as greenhouse gases, since they are capable of absorbing and holding heat in the atmosphere, thus contributing to a phenomenon known as global warming effect. Each of these gases is controlled by the Kyoto Protocol, which is a global environmental agreement. Fluorinated greenhouse gases are further controlled by specific European legislation.
Fluorinated greenhouse gases (F-GHG gases) are a group of fluorine-containing gases that have long atmospheric lifetimes and that trap heat in the atmosphere, including perfluorocarbons (PFCs), hydrofluorocarbons (HFCs), sulfur hexafluoride (SF6), and nitrogen trifluoride (NF3). Of all the greenhouse gases, fluorinated greenhouse gases are the most powerful and persistent greenhouse gases. Fluorinated greenhouse gases have very stable C—F bonds and, therefore, they are chemically very stable. Thus, they remain unchanged and stay for a long period of time if they are released to an ambient atmosphere. It is reported that the projected life span until consumption in the atmosphere for CF4 is 50,000 years, and for C2F6 is 10,000 years. Further, F-GHGs have high global warning potentials (GWP), which is a measure of the total energy that a gas absorbs over a particular time period. For example, it is reported that the global warming potential (relative to CO2) is 5,210 in the case of CF4 and 8,630 in the case of C2F6 (over a 20 year period).
Many industrial gas streams, such as exhaust gas streams produced by the manufacturers of semiconductor materials and devices contain a wide variety of chemical species. These chemical species must be removed from the gas streams before being discharged from manufacturing facilities into the atmosphere. Fluorinated greenhouse gases (F-GHG gases) are used during the manufacture of semiconductor materials and devices. For example, F-GHG gases, such as CF4, C2F6 and NF3, are used as cleaning gases to remove accumulated films, such as SiO2, from the surfaces of a chemical vapor deposition (CVD) chambers. F-GHG gases, such as CF4, C2F6, C3F8, C4H8, CHF3, SF6 and NF3, are used as etchants in dry etch processes. Furthermore, F-GHG gases are used in the production of DRAM, NAND and other semiconductor devices, including photovoltaic, display, MEMS, nanotechnology, and related device manufacturing.
Conventional methods of abating fluorinated greenhouse gases in a gas stream rely on a thermal combustion or decomposition of the fluorinated greenhouse gases, which methods typically takes place at a temperature of at least 1400° C. Thus, the conventional methods of treating fluorinated greenhouse gases in gas streams demand large amounts of energy.
Accordingly, there have been extensive efforts to develop methods and abatement systems for treating fluorinated greenhouse gases in gas streams that require lower amounts of energy.
U.S. Pat. No. 5,938,422 discloses a process for thermally destructing perfluorinated gases in an exhaust gas stream, wherein air/oxygen is added to a mixture of fuel gas and the exhaust gas stream prior to subjecting the mixture to combustion.
U.S. Pat. No. 6,126,906 discloses a method to remove perfluorinated gas from a semiconductor exhaust gas by thermally decomposing perfluorinated gas in the exhaust gas in a presence of saturated or unsaturated hydrocarbon gas, at a temperature of 600° C. or more under non-oxidative conditions (i.e., in the absence of separated oxygen gas).
U.S. Pat. No. 6,790,421 discloses a method of treating an exhaust gas by thermally decomposing fluorine-containing compound in the exhaust gas in a presence of γ-alumina catalyst and at least one decomposition-assisting gas selected from hydrogen gas, oxygen gas, and water vapor.
U.S. Pat. No. 7,347,980 discloses a process for treating fluorine-containing gases by contacting fluorine compound-containing gases with a catalyst in a presence of steam. The fluorine-containing gases are hydrolyzed to produce hydrogen fluoride (HF) gases. The use of catalyst allows the hydrolysis to take place at a temperature of from 400° C. to 800° C., which is much lower than the typical temperature of at least 1400° C. without the catalyst. The catalyst may be alumina, titania, zirconia and silica.